Method and device for overvoltage protection in dual-voltage vehicle electrical systems

ABSTRACT

The invention relates to a method and a device for overvoltage protection in dual-voltage vehicle electrical systems ( 1 ) which have a different level of voltage. According to the invention, a switching element (S 1,  S 2 ) is positioned in at least one branch of the vehicle electrical system on the higher voltage level and a voltmeter unit ( 3 ) is located in the vehicle electrical system on the lower voltage level, said switching element (S 1,  S 2 ) being controlled by the voltmeter ( 3 ).

[0001] The invention relates to a method and device for overvoltage protection in dual-voltage vehicle electrical systems.

[0002] Dual-voltage vehicle electrical systems of this type are well known in automotive engineering for example. Due to the increasing number of electric consumers, in many cases, one single voltage supply no longer suffices. Furthermore, the electric consumers used require higher operating voltage and/or higher electric power so that dual-voltage vehicle electrical systems with different voltage levels of 14V and 42V for example have been developed. It is also known to connect these vehicle electrical systems by way of a dc.-dc. converter so that they can be supplied via a common generator for example. A principle problem of such type dual-voltage vehicle electrical systems is that the electric consumers in the vehicle electrical system with the low voltage level have to be protected from static overvoltage conditions due to a short between the two vehicle electrical systems. This protection can be achieved for example in that the electric consumers in the vehicle electrical system with the low voltage level are provided with corresponding overvoltage protection elements that are designed to match the voltage in the other vehicle electrical system. The disadvantage of this way to proceed is that thus all of the electric consumers heretofore used in vehicle electrical systems with a low voltage level would have to be modified.

[0003] The technical problem underlying the invention is providing a device and a method allowing a greater ease of protecting the electric consumers in the vehicle electrical system with the lower voltage level from overvoltage conditions due to the other vehicle electrical system.

[0004] The solution to this technical problem becomes apparent in the subject matters featuring the characteristics of the claims 1 and 8. Further advantageous embodiments of the invention are recited in the subordinate claims.

[0005] For this purpose, a switching element is positioned in at least one branch of the vehicle electrical system on the higher voltage level and a voltmeter unit is located in the vehicle electrical system on the lower voltage level, said voltmeter unit being capable of switching off voltage branches in the vehicle electrical system with the higher voltage level by way of the switching element(s) upon detecting an overvoltage condition, thereby eliminating the cause of the overvoltage condition.

[0006] The switching elements can be arranged either in all of the branches which are non-critical with regard to safety or only in those branches in which there is, on account of the wiring, a serious risk of shorts with the other vehicle electrical system.

[0007] The voltmeter unit can be connected to the switching elements either via control lines or via a CAN bus or other bus systems.

[0008] In another preferred embodiment in which the two vehicle electrical systems are direct-coupled together by way of a dc.-dc. converter, the voltmeter unit is preferably integrated into the dc.-dc. converter.

[0009] The switching elements are preferably designed as semiconductor switching elements, more specifically as MOSFETs.

[0010] The method consists in measuring the voltage in the vehicle electrical system with the lower voltage level and in successively switching off, upon detecting an overvoltage condition, branches in the vehicle electrical system with the higher voltage by way of the switching elements, this step being performed until no overvoltage condition is detected any longer.

[0011] Particularly in the case of branches that have to be protected separately, like for example the left and right side of the vehicle lighting, the branches are switched off one after the other, the one branch being connected again prior to switching off the other one, so that there is always one branch remaining operative. For, if the overvoltage condition is still detected after the first branch has been switched off, this branch is not the cause of the overvoltage condition and accordingly, this branch can be connected again.

[0012] The invention will be described more explicitly below with reference to a preferred exemplary embodiment. The only FIGURE is a circuit diagram of a dual-voltage vehicle electrical system with overvoltage protection.

[0013] The dual-voltage vehicle electrical system 1 is comprised of a first voltage source U1 and of a second voltage source U2, whereby U2>U1. A dc.-dc. converter 2, which allows the vehicle electrical systems to be connectable in spite of the different voltage levels, is arranged between the two voltage sources U1, U2. In different branches, first electric consumers R4 are arranged in the first vehicle electrical system with the voltage source UI and second electric consumers R1-R3 are arranged in the second vehicle electrical system with the voltage source U2. A respective one of the switching elements S1 and S2 are arranged in the branch of the electric consumers R1 and R2. A voltmeter unit 3 measuring the voltage in the first vehicle electrical system is arranged in said first vehicle electrical system. The voltmeter unit 3 is connected to the control inputs of the switching elements S1 and S2. The electric consumers R3, in the branch of which no switching element is arranged, are for example safety critical consumers such as an electrical steering system or an electrical brake system, which are not allowed to be switched off. Furthermore, no switching elements need to be arranged in branches which, in the arrangement, are located far from the first vehicle electrical system.

[0014] The voltmeter unit 3 continuously measures the voltage in the first vehicle electrical system. If, for example, the branch of consumer R1 and that of consumer R4 short circuit, the voltmeter unit 3 detects the overvoltage condition in the first vehicle electrical system. Thereupon, the voltmeter unit 3 switches the first switching element Si so that the latter opens or closes respectively, switching off the branch of R1. In the example represented, the cause of the overvoltage condition is thus eliminated.

[0015] If, however, the voltmeter unit 3 still measures an overvoltage condition, the next switching element S2 is opened until there is no overvoltage condition any longer. The previously opened switching element S1 can hereby be closed first prior to opening the switching element S2. This way to proceed is particularly convenient in the case of consumers that have to be protected separately, since there is always one consumer remaining active. 

1. A device for overvoltage protection in dual-voltage vehicle electrical systems having different voltage levels, wherein a switching element (S1, S2) is positioned in at least one branch of the vehicle electrical system on the higher voltage level and a voltmeter unit (3) is located in the vehicle electrical system on the lower voltage level, said switching element (S1, S2) being controlled by the voltmeter unit (3).
 2. The device of claim 2, wherein a switching element is arranged in all of the branches of the vehicle electrical system that are non critical with regard to safety.
 3. The device of claim 1 or 2, wherein the voltmeter unit (3) is connected to the switching elements (S1, S2) by way of a bus system.
 4. The device of one of the previous claims, wherein the two vehicle electrical systems are connected by way of a dc.-dc. converter (2).
 5. The device of claim 4, wherein the voltmeter unit is integrated in the dc.-dc. converter (2).
 6. The device of one of the previous claims, wherein the switching elements (S1, S2) are designed as semiconductor switching elements.
 7. The device of claim 6, wherein the semiconductor switching elements are designed as MOSFETs.
 8. A method for overvoltage protection in dual-voltage vehicle electrical systems (1) having different voltage levels, involving the following steps: a) measuring the voltage in the vehicle electrical system with the lower voltage level and b) successively switching off voltage branches in the vehicle electrical system with the higher voltage level upon detecting an overvoltage condition in the vehicle electrical system with the lower voltage level until no overvoltage condition is detected any longer.
 9. The method of claim 8, wherein a switched off voltage branch is connected again in case an overvoltage condition is still detected after said branch has been switched off.
 10. The method of claim 9, wherein the switched off voltage branch is connected again prior to switching off the next voltage branch.
 11. The method of one of the claims 8 through 10, wherein certain voltage branches are simultaneously switched off and successively connected again. 